1. Field of the Invention
The present invention relates to a synthetic resin tube for bending use, which comprises a high-frequency induction heat generating member, and its bending method of performing a bending processing on this synthetic resin tube utilizing high-frequency induction heating.
2. Background of the Related Art
Today, heat set of tubes, made from thermoplastic synthetic resin and formed in various shapes, are used in a wide variety of fields.
For example, coil tubes, which are heat-set products of nylon and polyurethane tubes, are used as hose for industrial use, machine use or air tool use. Furthermore, tubes made through the two- or three-dimensional bending processing, are used as fuel pipe for an automotive vehicle or other pipes associated with various components in other industrial fields.
According to a conventional heat setting process for a thermoplastic resin tube, a pipe or tube is preheated or heated up to a desired temperature and then applied shaping processing, such as bending, under such a heated condition, followed by a cool-down processing by a cooling means, thereby manufacturing a desired heat-set product.
Heat surroundings were generally gas, fluid and solid (sand, dies or the like).
For example, in the fabrication of crank type tube, a pipe 1' is heated by a heating device H' as shown in FIG. 12(a), and thus heated pipe 1' is pushed or fitted into a die M' to form two bent portions N' and N' as shown in FIG. 12(b), and thereafter the pipe 1' is cooled down together with the die M', thus accomplishing a crank type pipe shown in FIG. 12(c).
As described above, the conventional heat-set product requires to heat not only the portion to be applied the two- or three-dimensional bending processing but the remaining portion other than such a bending portion before fitting into the molding die (sand, metal mold or the like). In particular, in the cooling down operation succeeding such a molding operation, the pipe united with the molding die as a whole needs to be cooled down, which results in deterioration of work effectiveness.
Unexamined Japanese Patent Application No. 69329/1989 discloses a method of bending a non-metallic tube, wherein a non-metallic tube to be bent, which contains granules having good electrical conductivity, is disposed near an induction coil which is actuated by supplying high-frequency current. Upon supply of high-frequency current to the induction coil, the granules in the non-metallic tube are inductively heated so that the temperature of the non-metallic tube reaches up to a predetermined temperature. Thereafter, bending processing is applied on thus heated non-metallic tube.
Furthermore, Unexamined Japanese Patent Application No. 249631/1988 discloses a method of manufacturing a fiber reinforced synthetic resin product. According to this method, light-weight reinforced fibers coated by thermoplastic resin are wound, together with metallic fibers, around a mandrel in layers utilizing the filament winding method, thus forming a fabricating material layer containing metallic fibers. Then, after the mandrel is removed, high-frequency induction heating is applied on the fabricating material layer to soften the thermoplastic resin, followed by deformation processing by which the fabricating material layer is bent and formed in a predetermined shape.